This is going to be too long and off-the-cuff, but...

I have a weakly-held theory that Overtraining Syndrome may be a neurological autoimmune disorder.

I have some personal experience from a very long time ago at a sub-elite level with this as I was diagnosed with the classic ectopic arrhythmia sign where several doctors told me to stop ALL training, and I know of at least one other case that caused the retirement of a reigning world champion. The muscle feeling for me was that training results in numbness, no longer soreness, which was weird and felt like under-training. I do think that poor sleep and anemia were primary factors just as the athlete in the podcast.

To explain, I will go into some uncommon detail about training and recovery. Training starts with adrenaline, and results in a lot of protein breakdown. Recovery begins with the immune system picking up these proteins and releasing prostglandins and other hormones to create inflammation and suppress macrophages from the immune system. Without sufficient suppression, you get damage, most of which can be reversed quickly with local satellite cells, but nerves are harder to repair, which is why you see long-term nervous system manifestations of most autoimmune disorders. Also note the NSAID link. This is theory connecting some dots, but the feeling is where it started. Hard to explain: difficulty engaging strength, burning pain and tingling etc.

I also want to make a different point about the training cycle that they mention. The pull-down pop-up phenomenon, which is the cycle of training, then rest, then higher performance, occurs over a few days, and is almost entirely due to increasing neurotransmitter levels. In simple terms, you are teaching your body to go harder, but the actual muscles aren't changing much. Actual muscular adaptation requires much longer timeframes. If you are just starting any exercise, your fist improvement is your form, then your adrenaline, then your glycogen capacity, then your insulin sensitivity, then your lung efficiency, then your heart vascularization, then your sweat glands, then your bodyweight, then your muscle fiber density, then your muscle fiber quantity. That timeline is somewhere from years to decades, and only the inflammation and adrenaline works on that short-term cycle. Put another way, your physical capacity is not greatly improved after one week of training-recovery cycle. It's actually surprising how little of each season's improvement actually survives a month off, but yet how much a decade of elite training survives years of rest. This is controversial, but if your goal doesn't require near-max performance, then you can ignore the short-term cycle. For instance, to lose weight, it's best not to use this cycle because recovery is much longer in caloric deficit, and you can burn many more calories with low intensity every day rather than high intensity with rest days. This gets more nuanced with goals from other points in the progress timeline.

Another point I'd like to make related to the above, and the podcast. A lot of top-level coaches really suck at training athletes. Even at the olympic level, coaching has a lot more to do with organization, motivation, maybe manipulation, and ultimately selection. That's a separate skill set, and you can make a pretty good team by pushing a large group to their limits until only the best remain. It's not the same thing as getting the best performance out of each individual, which is why it sounds so crazy from her perspective. A top athlete is likely to seek out an independent performance coach after making it through the olympic program filter, and I think this has a lot to do with why the same people keep coming back. They're past the filter and training for performance, not constantly being tested. I think the worst sport for bad coaching might be swimming: endless long sets all season with distance and sprinters mixed into the same lane and then a month of restful performance training at the end. Jason Lezak famously swam the fastest 100 leg in history well past his prime by training himself alone mostly with 50s on a minute. Okay that's far enough off the topic. Peace.